This invention concerns apparatus for encoding auxiliary image information in a widescreen television system of the type including an auxiliary subcarrier for conveying auxiliary information.
A conventional television receiver, such as a receiver in accordance with NTSC broadcast standards adopted in the United States and elsewhere, has a 4:3 aspect ratio (the ratio of the width to the height of a displayed image). Recently, there has been interest in using higher aspect ratios for television receiver systems, such as 2:1, 16:9 or 5:3, since such higher aspect ratios more nearly approximate or equal the aspect ratio of the human eye than does the 4:3 aspect ratio of a conventional television receiver.
It is desirable for widescreen television systems to be compatible with conventional television receivers to facilitate the widespread adoption of widescreen systems. It is also desirable to have such a compatible widescreen system with provisions for enhancing or extending the definition of a displayed image so as to provide extra image detail. Such a widescreen EDTV (extended definition television) system is described by M. A. Isnardi et al. in an article "Encoding for Compatibility and Recoverability in the ACTV System", published in IEEE Transactions on Broadcasting, Vol. BC-33, December 1987, and in U.S. Pat. No. 4,855,811 of M. A. Isnardi.
In the Isnardi et al. system, an auxiliary subcarrier is quadrature modulated with first and second auxiliary signals. One of the modulating auxiliary signals contains extra horizontal high frequency luminance information for enhancing image detail. The other modulating auxiliary signal contains time expanded left and right side panel components including high frequency chrominance and luminance information. Low frequency side panel chrominance and luminance information is time compressed into an overscan region of a main signal component containing center panel information.